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Temperature Classification

All products certified suitable for use in a hazardous area, whether they be instruments, enclosures, luminaries etc should be marked with their temperature class. The temperature class defines the maximum surface temperature the product is allowed to operate at. Temperature class is referenced to an ambient of -20°C to +40°C unless specifically indicated otherwise.
According to the type of explosion protection used on the product e.g. Exd, Exe etc, the temperature corresponds either to the maximum temperature of the external surface of the product, or to the maximum temperature of the internal surface of the product.
When selecting a product, ensure the temperature class of the product is below the minimum ignition temperature of the explosive atmosphere where it will be installed.
North American and Canadian practice differs from that used in Europe with smaller temperature ranges being allowed in the new world.
 
Temperature Classification
Max. Surface
Temp °C
North AmericanEuropean
450T1T1
300T2T2
280T2A---
260T2B---
230T2C---
215T2D---
200T3T3
180T3A---
165T3B---
160T3C---
135T4T4
120T4A---
100T5T5
85T6T6

 
The European codes allow for a Small Component Relaxation as below;
 
Surface Area T4 Classification
< 20mm2Surface temperature < 275°C
>20mm2 <10cm2 Surface temperature <200°C
>20mm2 Power dissipation <1.3 W at 40°C ambient
Power dissipation <1.2 W at 60°C ambient
Power dissipation <1.0 W at 80°C ambient




Electrical Installations in Hazardous Areas



Practical Electrical Equipment and Installations in Hazardous Areas


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